Chinese Utility Model Application No. 201420867174.3 discloses a headrest adjusting support which includes two linkage assemblies and a linear driving device located between the linkage assemblies. An output end of the linear driving device is connected with the linkage assemblies via a driving rod, so that a fastener of the linkage assembly is driven to rotate by means of linear reciprocating motion, thereby the height and the angle of the headrest can be adjusted.
However, the headrest adjusting support has some drawbacks. For example, the linear driving device is located in the middle, the linkage assemblies at both sides are driven only by the driving rod, thus the balance of the support is poor, and the support force is not strong. In actual operation, since the width of the headrest is big, and sitting position of user is not fixed, thus loading forces at two sides of the headrest are different, which causes one linkage assembly endure a larger loading force, while the other linkage assembly endure a smaller loading force. Furthermore, the driving rod at the middle cannot balance them, as a result, the movement ranges of both linkage assemblies are different, which causes the headrest deflect, even generates damages on the sofa structure.
Thus it's necessary to provide an improved lifting device for headrest which has better balance.